Abstract: Unlike heatpipes which typically use water under a slight vacuum for working fluid, the Revo heatsink is slightly pressurized with a fluorocarbon called R134a. R134a has a boiling point of -26.3°C at room pressure, but in the hermetically sealed system at a slight pressure that boiling point is raised to a level more appropriate for this application.

Akasa's Revo heatsink is known as a Loop Thermosyphon Cooler; it functions along the same lines as a heatpipe but relies on gravity instead of capillary forces to return its 'working fluid' back to the hot side. The working fluid is what conducts heat absorbed by the heatsink, from the processor to the heat exchanger, where forced air passing over cooling
fins removes it to the surrounding environment.

Unlike heatpipes which typically use water under a slight vacuum for working fluid, the Revo heatsink is slightly pressurized with a fluorocarbon called R134a. R134a has a boiling point of -26.3°C at room pressure, but in the hermetically sealed system at a
slight pressure that boiling point is raised to a level more appropriate for this application.
An example of this is those 'Air Duster' cans we all use to clean keyboards with.

Outwardly the Akasa Revo heatsink looks like a self-contained watercooling
system (ie. Corsair H50 ), but unlike a water
cooling system it does not use any kind of mechanical or electrical pump
to move its working fluid from hot to cold sides. The Revo heatsink
is also surprisingly lightweight - the entire device weighs just 330
grams!

Frostytech will
explain how it all works in
just a moment, it's really quite a fascinating bit of thermodynamics. First let's touch on the
regular heatsink specs and stats.

As far as regular heatsinks go the Akasa Revo installs
onto Intel socket 775 and AMD socket 939/AM2/AM3 processors just like any other
CPU cooler. Aside from the one requirement that it be oriented properly, there
are no other special requirements to its use. The Revo heatsink stands 137mm
tall, is equipped with a single 92mm PWM fan that operates at 2200-600RPM and
the whole unit weighs a feathery 330 grams. It's hermetically sealed so it never
needs to be refilled, there is no pump motor to make noise and the thermosyphon
action itself is entirely passive and virtually silent.

When the
R134a working fluid is heated by the processor in the evaporator chamber at the
base of the Revo heatsink it begins to boil and change phase from
liquid to vapour. The evaporated working fluid exits the 'evaporator chamber'
from the top carrying with it heat and travels up to a 'condenser' via the
'rising tube.'

Externally, forced air from a fan is blown on the condenser
(aka liquid-to-air heat exchanger) to cool it and remove the heat to the
surrounding environment. This drops the temperature of the working fluid enough
for it to condense back to a liquid, which then exits the condenser and
returns to the evaporator chamber by gravity through the 'falling tube'. The whole
cycle then repeats itself continuously.

Thus, there are four critical parts to a Loop
Thermosyphon Cooler;

1) The 'evaporator chamber' where heat is conducted away
from the CPU (above).

3) The 'condenser' or heat exchanger where the working fluid is cooled back
to liquid phase (above).

4) The 'falling tube' where the working fluid returns by gravity to the
evaporator chamber.

Akasa Revo is Orientation Specific

Incorrect orientation of the heatsink can impede
the return of working fluid back to the evaporator, effectively causing the
Thermosyphon to stall and send temperatures suddenly straight through the roof.
The Akasa Revo heatsink must therefore be
installed in a horizontal orientation as per the instructions for it to function
properly - the heat exchanger must be above the CPU
block.

According
to documentation from NoiseLimit, the original designer of the Revo
heatsink and SilentFlux technique, the company worked to address orientation issues
by using a one-way flow valve and encouraging 'flow boiling' rather
than 'pool boiling' within the evaporator chamber. Since any puncture of the
cooling loop would render this heatsink completely useless, we can't show you what it
looks like on the inside.

Brackets and Installation Hardware

The heatsink installs onto
Intel and AMD motherboards with a set of custom plastic heatsink retention cages
that first must be mounted to the board. One is for Intel Socket
775 boards and the other for AMD socket 754/939/940/AM2/AM3 platforms.

The Intel socket 775
bracket uses the standard push-to-lock plastic clips that insert into the four
motherboard holes around the processor socket. For AMD processors, the
custom bracket engages the central lug on the socket 754/939/940/AM2/AM3
heatsink retention cage.

FrostyTech's Test Methodologies
are outlined in detail
here if you care to know what equipment is
used, and the parameters under which the tests are conducted. Now let's move
forward and take a closer look at this heatsink, its acoustic characteristics,
and of course its performance in the thermal tests!